It was just called Jenson. There were five weights going from Light to Black and Letraset had only Medium and Extra Bold. It seems to have originated in the Seventies, but I don't know who designed it. The Letraset catalog is mum on the subject (usually they give credit). I'm pretty sure it's not related to ATF Jenson.

Mark is correct - Jenson in 1928 ATF Specimen Book looks nothing like the Letraset Jenson. My 1986 Letraset Catalog lists no designer and only medium and extra bold weights. Has it been digitized? - That is the question?

I wouldn't call it Letraset Jenson as it didn't originate with them (they only have two weights, remember?). It looks a bit like something Les Usherwood may have done, but if that were the case, I think Letraset would have given credit as they did with his other designs.

Headliners had a very similar (identical?) font called neo-Jenson which may be where it originated. It's difficult to tell with them whether a font is their original design or their version of an existing design since they added the "neo-" prefix onto both.

I wonder if it was Freda Sack... a Google search unearthed the following...

"British designer Freda Sack was born in London in 1951 and gained a diploma in graphic design and typography from the Maidstone College of Art. Her first job, in 1972, was with Letraset International where she worked as a photographic retoucher, later moving into their type studio. Under the supervision of Bob Newman she learnt the skills of drawing type and stencil cutting, and began to design headline faces. She became involved in producing artwork for the Letraset instant lettering dry transfer sheets, and trained junior designers."

and she has since designed Jenson Old Style bold condensed (with Colin Brignall, 1982)